Grappling Dummy: Legitimate Self Study?

I am hoping to start BJJ training in about six months, after I get some things worked out. Earlier today I had the idea to build a grappling dummy, and searching the basic and advanced grappling forums hasn't led to a direct answer to my questions:

Can an untrained individual get any real benefit from a grappling dummy?

How tall should I make the dummy relative to my own height (I'm 5′7″)?

Is an area roughly 4′ by 7′ large enough to work in?

I figure that even if I never get to train BJJ, grappling drills would be a good workout for me since I wouldn't have to worry about falling (I have impaired balance). Hell, even getting into certain positions would help increase my flexibility and/or coordination (e.g. triangle choke, moving from closed guard to high guard, et cetera).

Does this fall under the category of “Don't try to learn from books,” or is this legitimately justifiable?

I could see it being a useful tool for someone who already knows what they're doing in conjunction with real classes. For someone who hasn't even started training yet.. thats crappling dude.

"Boxing is the art of hitting an opponent from the furthest distance away, exposing the least amount of your body while getting into position to punch with maximum leverage and not getting hit."
Kenny Weldon

Never trained with a dummy but I can't see how useful it would be to practise with something that wont respond to your movements. At the very least you would be better off training with a friend but the best option for a beginner is to train with someone who knows what they are doing. Otherwise you could be wasting your time with poor, ineffective technique or worse yet ending up injuring yourself.

And how embarrassed would you be to be found injured on top of a rubber doll?

I use a grappling dummy to drill submissions on when I'm not training. There are some pictures of it in this thread.

I did most of the Gracie Combatives stuff with it. It went pretty well, and I think you can get a pretty good idea of the moves on it. The way the Gracie's laid out the instruction really helps. They explain stuff to the point of almost over doing it.

Problems with it: the dummy doesn't try to pull his arm out while it is sweaty and you are trying for an armbar from the guard. So you may not know to squeeze the knees from this position. However, once someone does it to you a few times, you will learn. You don't have someone looking at you and correcting form. Like raising your hips too high or positioning your head too far forward.

I first made mine to suppliment the drilling that I wanted to do in between class. If I didn't have people come by, I could still drill figure 4 arm locks, arm bars, chokes, and pretty much and submission you can come up with. It is great for that.

Mine was pretty cheap to make, and I do think it is better than nothing but worse than live partners. It is kind of like working the heavy bag. Really good for you after you have been taught to do the techniques right. But could be bad, and cause injuries if you have not been shown how to do those techniques.

[*]Can an untrained individual get any real benefit from a grappling dummy?

No, an untrained person will usually be doing themselves a disservice by attempting techniques before getting proper instruction.

There are a lot of fine details that separate moves from the crappling, ok, proficient, and perfect categories. You're going to have to drill moves many in order to develop a proper kinetic sense and proficiency, and if you develop bad habits early you're going to have to spend a lot more time fixing what's ingrained in your head.

IMO learn from a qualified instructor first, then practice drills on the dummy after you know the details.

[*]How tall should I make the dummy relative to my own height (I'm 5′7″)?

Well, the consensus of people I certainly trust as authorities is that I shouldn't do it—so I'm not going to do it. This is exactly why I started this thread: I'm ignorant of fine details and, thus, couldn't see why this would be a bad strategy.

What part of not reading what people actually wrote and necroing a thread without adding anything useful seemed like a good idea?

Just curious.

Wow, I think this is the first time one of my threads has been necro'd.

Since technique forum rules require me to post something remotely useful, I'll take this opportunity to point out that I'm no closer to training BJJ than I was when I started this thread; I had to delay my six month plan by about six months.